Because there is an increasing demand for high density assembly of electronic components in various fields of electronic equipment, recent circuit designs have increasingly utilized surface mounted semiconductor devices. Surface mounted semiconductor devices are smaller than conventional semiconductor devices and thus take up less space on a printed circuit (PC) board. Consequently, it becomes important to efficiently dissipate heat generated from the electronic components mounted on the PC board.
For example, transistors are commonly packaged in surface mount cases. The device's case includes a metallic backing which is soldered to a heat pad or heat sink on the PC board. Unlike conventional heat sinks, a heat sink for a surface mounted device consists of a thin layer of metallic material on the top surface of the PC board. The technical data sheet for a typical surface mounted transistor contains two power dissipation values. The first power dissipation (P.sub.D1) reflects the maximum power that the device can dissipate with a heat sink having the recommended dimensions. For example, a typical P.sub.D1 value is 1.56 watts when the ambient temperature is 25.degree. C. The second power dissipation value (P.sub.D2) reflects the maximum power that the device can dissipate when the device's case is held at a specific temperature. For example, a typical device may be capable of dissipating 15 watts if the case temperature is held at 25.degree. C. Thus, as can be seen, if the case is held at a lower temperature, the device can dissipate up to 10 times the power. However, the technical data sheets include no suggestions as to how to keep the case temperature down at that level.
The present invention is directed to overcoming one or more of the problems, as set forth above.